<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>图标的引用</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">

  </head>
  <body>
    <div class="dropdown">
      <button class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
        <!-- <span class="glyphicon glyphicon-home"></span> -->
        This is a Button.
        <sapn class="caret"></sapn>
      </button>

      <ul class="dropdown-menu">
        <li><a href="#">Home</a></li>
        <li><a href="#">Next</a></li>
        <li><a href="#">Pre</a></li>
        <li><a href="#">First</a></li>
        <li><a href="#">Last</a></li>
      </ul>

    </div>
    <!-- jQuery文件。务必在bootstrap.min.js 之前引入 -->
    <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
    <!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
    <script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
  </body>
</html>
